Description: Allophane is a clay mineral with the general chemical composition of kaolinite but lacking a crystalline structure. It is formed by the breakdown of other alumino-silicates, such as feldspar, due to weathering or hydrothermal alteration.

DODGE COUNTY: A colorless, banded isotropic mineral found in the matrix of the Neda iron ore was tentatively identified as allophane by Hawley and Beavan (1934) based on optical and microchemical tests.